maven 3 archetype:generate Error

I followed the instructions on Apache Maven site and it works fine but during the tutorial i was asked to type in the below c开发者_如何学Pythonode, what does that mean and why does it keeps throwing me a build error?. However i tried to type single line everytime and also everything together nothing makes a difference. Could some one please help me interpret this one and how to get started with maven without errors?

Thanks a lot, SS

 mvn archetype:generate \
  -DarchetypeGroupId=org.apache.maven.archetypes \
  -DgroupId=com.mycompany.app \
  -DartifactId=my-app

error below [UPDATE] , Updated the title also.

Thanks for your responses. I found the problem, i was behind a proxy and did not know the proxy feature in maven and as it was running for the first time, it was trying to download some plugins and failed. now i fixed it and it works as it should.

Thanks, SS